Tanning of hides and skins with formals



Patented Dec. 4, 1951 TANNING OF HIDES AND SKINS WITH FORMALS Robert C. Putnam, Marblehead, Mass., assignor to United Shoe Machinery Corporation, Flemington, N. J., a corporation of New Jersey No Drawing. Application March 5, 1948, Serial No. 13,330

6 Claims.

My invention relates to the treatment of hides and skins.

In the well-known chrome tanning process, a skin or hide pretreated to remove hair and treated by various other steps such as bating and pickling, is immersed for an extended period in a solution of basic chromium sulphate. Ordinarily this chromium treatment of the skin or hide is carried on in a paddle or a drum during the chrome treating period and is then removed from the paddle or drum and aged for a period of from several hours up to two days.

In the vegetable tanning process, dehaired and otherwise pretreated skins or hides are subjected to various steps including a prolonged soaking treatment in a solution containing various vegetable extracts. Tanning by the vegetable method occupies a period of several weeks and involves extensive handling of the hides.

By either of these common methods of tanning, extended periods of time are required so that to insure continuous production of leather a very large number of skins or hides must be maintained in various stages of tanning. Investment in skins or hides and in treating tanks, vats, or

other treating equipment is large so that cost of the ultimate leather is high.

It is an important feature of my invention to convert skin and hide material to a stable nonputrescible leather-like condition by a short and simple treatment of the skin or hide materials with a new type of reagent. By my new process there is formed a tough, pliable product similar to leather in appearance and in many other properties. The new product will withstand prolonged soaking in water without marked shriveling or hardening even at relatively high temperatures, and is exceptionally resistant to mold growth.

' I have discovered that skins or hides may be converted to this novel, leather-like material by drying the skin or hide material and contacting the dried material with an organic solvent solution of a formal containing a limited amount of a strong mineral acid.

For treatment according to the process of the present invention, I have found that bated or pickled skins or hides, for example calfskins or steer hides, are satisfactory. Skins or hides in other conditions may also be used.

Skins or hides of animals generally used for the making leather may be treated according to the process of the present invention. In the specification, the terms skin and skin material are to be understood in their broad sense as including these materials. The term hides in the claims is intended to include both hides and skins in condition for conventional tanning.

Where a pickled material is used, it is first subjected to a conventional depickling operation. The depickled skin is then immersed in water with agitationto remove dissolved salts and other soluble materials. A suitable treatment period may range from around two hours for calfskin to four hours for a steer skin.

The depickled and soaked skin is then dried to a moisture content which may be between about 10 and about 15%. This moisture content is determined by comparison with the weight of the skin when subjected to a further drying for sixteen hours in air at 105 C. It has been found that drying is most satisfactorily accomplished by the action of solvents, for example, acetone, methyl acetate, isopropyl alcohol, dioxane, methyl Cellosolve acetate or other solvent which will remove the water without seriously harming the skin. This drying may be effected by leaving the skin immersed in an agitated bath of the solvent overnight. The solvent is then removed from the skin, suitably by evaporation in a stream of dry, warm air.

The above is but one of many conceivable methods for treatment of a skin prior to the treatment with my new agents. Modifications will be readily apparent to persons familiar with the handling of skins. For example, a bated skin need not be subjected to the depickling and washing operations above outlined.

The dried skin is immersed in a body of the liquid treating agent and is maintained in the liquid for a sufficient period to convert the skin to the new leather-like condition.

The liquid treating agents according to my invention comprise organic solvent solutions of a strong mineral acid and a formal. Formals whichhave been used for the treatment of skin material in accordance with my invention include the formal of the monomethyl ether of diethylene glycol, the formal of the monomethyl ether of ethylene glycol, the formal of the monobutyl ether of diethylene glycol, di-chlorethyl formal,

methoxy methylal, ethyl formal, butyl formal, dibutoxy methane and glycol formal. These formals may be considered as having the formula wherein R is an aliphatic organic radical containing more than one carbon atom. For efficient operation in my process, the formals may be used to the extent of about 2% to by volume, based on the volume of the solution.

Among the strong mineral acids which may be used are sulfuric acid, hydrochloric acid, hydrobromic acid, and perchloric acid. Other strong mineral acids may be used. These acids may be employed in the proportions of about 0.3% to about 4% of a concentrated solution of the strong mineral acid base on the total volume of the treating agent. Concentrated hydrochloric acid Will contain about 38% of HCl; concentrated sulfuric acid will contain about 90% of H2804; concentrated hydrobromic acid will contain about of I-IBr;. and concentrated perchloric acid will contain about HC1O4. The term in the claims, concentrated aqueous solutions of strong mineral acids, refers to aqueous solutions containing the above noted percentages of these acids. The required volume of concentrated acid may be diluted before mixture with the remaining components where it is desirable to avoid excessive interaction with the remainder of the treating agent. In the treating agent, the formal is employed in the ratio of about 5 to 15 parts by volume to one part by volume of the concentrated strong mineral acid.

Suitable solvents for use in the treating agent include acetone, di-oxane, and trichlorethylene. Other similar neutral organic solvents such as methyl, n-propyl ketone or other solvent for the formal may be used.

The time of immersion of the skin in the treating agent varies with the weight and type of skin treated. Preferred times of treatment may be from about one-half hour to about five hours. In the case of a calfskin, satisfactory action has been obtained by immersion of the prepared, dried, calfskin for about two hours at room temperature in a solution comprising 1% by volume of a 38% hydrochloric acid solution, 9% by volume of the formal of the monomethyl ether of diethylene glycol, and 90% by volume of acetone.

The temperature of the treating bath may vary. Factors controlling the temperature include the boiling points and vapor pressure of the solvents and of the treating agents and the rate of treating action desired.

After the above treatment, the skin is removed from the treating bath and is immersed in a solvent to remove soluble materials such as excess agent, reaction products and the like. Suitable solvents for this use are tri-chlorethylene, acetone and toluene.

The skin is removed from the solvent bath and is permitted to dry. The dried skin is then placed in a neutralizing bath, which may be a depickling solution, until it reaches a pH of about 7 or other value depending upon the properties desired. This step is desirable in that it also serves. to neutralize or decompose acid compounds within the skin. The skin is finally washed to remove salts, and is then removed from the washing bath.

The treated skin may be subjected to such fur- 90 parts by volume of acetone.

ther treatments as desired, for example, dyeing, fat liquoring or stuffing, drying and surface finishing.

The following examples are given as illustrative of processes in accordance with the present invention. It is to be understood that the invention is not restricted to the reagents and procedural details disclosed in these examples.

Example 1.--A bated and pickled calfskin was depickled by immersion for one'hour in a 5% aqueous solution of sodium bicarbonate. The depickled calfskin was then washed in running water for an hour and dried overnight in acetone. The calfskin was then removed from the acetone, subjected to a blast of warm air to evaporate the acetone and then immersed for two hours in a treating bath at 130 F., the treating bath consisting of 1 part by volume of concentrated (38%) hydrochloric acid, 9 parts by volume of the formal of the monomethyl ether of diethylene glycol and The treated material was then removed from the bath, washed in acetone for two hours, removed from the acetone and allowed to dry. It was then immersed in a 5% solution of sodium bicarbonate in water until the skin reached a pH of about 7. The neutralized skin was removed from the neutralizing oath and washed in running Water for two hours. At this time the calfskin was found to be in a stable, nonputrescible condition in which it could be subjected to the usual operations following tanning.

Emmple 2.A bated calfskin was immersed overnight in acetone to dry it to a moisture content of about 10% determined as noted above. The dried calfskin was then removed and the acetone was evaporated by a blast of warm air. After evaporation of the acetone the calfskin was immersed in a treating bath at 130 F. for two hours, the bath consisting of 1 part by volume of concentrated (38%) hydrochloric acid, 9 parts by volume of 2,2 dichlorethyl formal and parts by volume of acetone. The treated skin was then removed and washed for two hours in a bath consisting only of acetone. The skin was then removed from the acetone, the acetone evaporated and the skin then immersed in a bath of 5% solution of sodium bicarbonate in water until the skin reached a pH of about 7.. The neutralized skin was removed from the sodium bicarbonate solution and placed in a bath of running water for two hours, at which time it was removed and found to be in a condition resembling leather in which it could be subjected to the usual operations following tanning.

Example 3.A bated and pickled steer hide was immersed overnight in acetone to dry the hide to a moisture content of about 10% calculated as noted above. It was then removed and the acetone evaporated. by a blast of warm air. The dried hide was then treated in a bath consisting of 10 parts by volume of concentrated (38%) hydrochloric acid, 30 parts by volume of the formal of the monomethyl ether of diethylene glycol and 60 parts by volume of acetone. The treatment was carried out at F. for aperiod of five hours. The treated hide was removed from the bath and washed for two hours in acetone and was then removed and the acetone allowed to evaporate. The hide was neutralized by soaking in a bath of 5% sodium bicarbonate in water until the skin reached a pH of about '7. The neutralized side was removed and soluble materials removed by washing it in a bath of running water for two hours. The hide was found to be in a stable and nonputrescible condition suitable for conventional after-tanning treatment. Example 4.-A bated and pickled calfskin was immersed overnight in acetone to dry the skin to moisture content of about 10% calculated as noted above. It was then removed and the acetone evaporated by a blast of warm air. The dried skin was then treated in a bath consisting of 1 part by volume of concentrated (38%) hydrochloric acid, 9 parts by volume of dibutoxymethane, and 90 parts by volume of acetone. The treatment was carried out for a period of two hours at 130 F. Then the treated skin was removed from the bath and washed for two hours in acetone and was then removed and the acetone allowed to evaporate. The skin was neutralized by soaking in a bath of a 5% solution of sodium bicarbonate in water until the skin reached a pH of about 7. The neutralized skin was removed from the sodium bicarbonate and placed in a bath of running water for about two hours, at which time it was removed and found to be in a condition in which it could be subjected to the usual operations following tanning.

Example 5.A bated and pickled steer hide was immersed overnight in acetone to dry the hide to a moisture content of about calculated as noted above. The dried hide was then removed and the acetone evaporated by a blast of warm air. After evaporation of the acetone, the steer hide was immersed in a treating bath at 130 F. for about five hours, the bath consisting of 1 part by volume of concentrated sulfuric acid, 9 parts by volume of the formal of the monomethyl ether of ethylene glycol and 90 parts by volume of acetone. The treated hide was then removed from the treating bath and washed for two hours in acetone. The hide was then removed from the acetone, the acetone evaporated and the skin then immersed in a bath of 5% solution of sodium bicarbonate in water until the hide reached a pH of about '7. The neutralized hide was removed from the sodium bicarbonate solution and placed in running water for two hours, at which time it was removed and found to be in a condition in which it could be subjected to the usual operations following tanning.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:

l. The method of tanning hides which comprises drying the hide by immersing the hide in a water miscible inert organic volatile solvent, then removing the solvent to obtain a moisture content of from 10% to based on the dry weight of the hides and immersing the hides in a solution containing an inert organic solvent, from 0.3% to 4% by volume of a concentrated aqueous solution of a strong mineral acid, and at least 2% by volume of a formal having the formula wherein R is an aliphatic radical containing more than one carbon atom, the formal being present in the ratio of from 5 to 15 parts by volume to 1 part by volume of the acid.

2. The method of tanning hides which comprises drying the hide by immersing the hide in a water miscible inert organic volatile solvent, then removing the solvent to obtain a moisture content of from 10% to 15% based on the dry Weight of the hides and immersing the hides in 6 a solution comprising an inert organic solvent, from 2% to 30% by volume of a formal having the formula /O-R HgC wherein R is an aliphatic radical containing more than one carbon atom, and from 0.3% to 4.0% by volume of a concentrated aqueous solution of a strong mineral acid, the formal being present in the ratio of from 5 to 15 parts by volume to 1 part by volume of the acid.

3. The method of tanning hides which comprises drying the hides by immersing the hide in a water miscible inert organic volatile solvent. then removing the solvent to obtain a moisture content of from 10% to 15% based on the dry weight of the hides and immersing the hides in a solution comprising an inert organic solvent, from 2% to 30% by volume of the formal of the monomethyl ether of diethylene glycol, and from 0.3% to 4% by volume of a concentrated aqueous solution of a strong mineral acid, the formal being present in the ratio of from 5 to 15 parts by volume to 1 part by volume of the acid.

4. The method of tanning hides which comprises drying the hide by immersing the hide in a water miscible inert organic volatile solvent, then removing the solvent to obtain a moisture content of from 10% to 15% based on the dry weight of the hides and immersing the hides in a solution comprising an inert organic solvent, from 2% to 30% by volume of the formal of the monomethyl ether of ethylene glycol, and from 0.3% to 4% by volume of a concentrated aqueous solution of a strong mineral acid, the formal being present in the ratio of from 5 to 15 parts by volume to 1 part by volume of the acid.

5. The method of tanning hides which comprises drying the hide by immersing the hide in a water miscible inert organic volatile solvent, then removing the solvent to obtain a moisture content of from 10% to 15% based on the dry weight of the hides and immersing the hides in a solution comprising an inert organic solvent, from 2% to 30% by volume of dibutoxy methane, and from 0.3% to 4% by volume of a concentrated aqueous solution of a strong mineral acid, the dibutoxy methane being present in the ratio of from 5 to 15 parts by volume to 1 part by volume of the acid.

6. Themethod of tanning hides which comprises drying the hide by immersing the hide in a water miscible inert organic volatile solvent, then removing the solvent to obtain a moisture content of from 10% to 15% based on the dry weight of the hides and immersing the hides in a solution comprising an inert organic solvent, from 2% to 30% by volume of a formal having the formula wherein R is an aliphatic radical containing more than one carbon atom, and from 0.3% to 4% by volume of a concentrated aqueous solution of a strong mineral acid, the formal being present in the ratio of from 5 to 15 parts by volume to 1 part by volume of the acid, for a period corre sponding to from about two hours for calfskin to about four hours for a steer hide, removing uncombined compounds by the action of a solvent,

ROBERT C. PUTNAM.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number FOREIGN PATENTS Country v Date France Nov. 2, 1908 Great Britain Mar. 23, 1938 Australia Jan. 9, 1943 OTHER REFERENCES "Journal of American Leather Chemists vol. 38, May 1943, page 185. Article by Roddy.

Formaldehyde, by Walker, page 139 (Rhei'n hold Pub. C0rp., N. Y. C.), 1944. Copy in Division 31.

Organic Chemistry, Whitmore, page 255, D. Van Nostrand 00. N. Y. C., 1937, Copy in Division Number 

1. THE METHOD OF TANNING HIDES WHICH COMPRISES DRYING THE HIDE BY IMMERSING THE HIDE IN A WATER MISCIBLE INERT ORGANIC VOLATILE SOLVENT, THEN REMOVING THE SOLVENT TO OBTAIN A MOISTURE CONTENT OF FROM 10% TO 15% BASED ON A MOISTURE WEIGHT OF THE HIDES AND IMMERSING THE HIDES IN A SOLUTION CONTAINING AN INERT ORGANIC SOLVENT, FROM 0.3% TO 4% BY VOLUME OF A CONCENTRATED AQUEOUS SOLUTION OF A STRONG MINERAL ACID, AND AT LEAST 2% BY VOLUME OF A FORMAL HAVING THE FORMULA 